When \(O\)  'successfully' maintains content it should preserve perceptually important edges from \(C\)  (i.e. humans asked to label the boundaries between perceptually distinct regions, as in the labeling of the BSDS dataset [1]}, would label roughly the same contours in the content and the stylized output) and regions with similar textures in \(C\)  should take on similar textures in \(O\)  (although this last quality isn't always desirable, for example when \(S\)  is a cubist style). While the explicit definitions of style and content used by various style transfer algorithms can dramatically differ from this interpretation, in my experience outputs which humans perceive as `good', `compelling', or `successful' tend to share the above characteristics.
